Crowded conditions require slowing and stopping
Aliases: crowd-aware stopping · density-adaptive speed · congested-space navigation
What it is
Density-adaptive robot speed and stopping reduces speed as crowds erode free space, visibility, and prediction time, and holds a stop when clearance cannot be assured. It is not a lookup from head count to one speed. Occlusion, relative motion, escape space, and braking margin jointly determine whether proceeding remains safe.
Why it happens
Crowding couples pedestrian trajectories through mutual avoidance, making a person's history less predictive. Body occlusion also shortens the interval between first observation and path entry. Lower speed reduces travel during system delay and lowers collision energy while allowing new sensor observations. If no verified stopping corridor remains, even slow creeping delegates avoidance to pedestrians; stopping is the controlled state.
Studying it
Simulation and controlled crowds can vary density, cross-flow, occlusion, and robot speed independently. Measures include minimum time-to-collision margin, hard stops, close body-space intrusions, throughput, and forced pedestrian detours. Trajectories should be stratified by local density and visible free space rather than arena-wide head count. Field logs add near misses and prolonged blockage, but safe stops, planning deadlock, and sensing failure need separate labels. An absence of collisions is not sufficient evidence.
Where it stops holding
Density alone is not a sufficient hazard indicator: a stable same-direction queue can be more predictable than sparse high-speed crossing. Children, carts, or corner occlusion can create high risk at low counts. A stopped robot may obstruct an exit or induce squeezing, so its refuge position must preserve evacuation and accessible routes. Resumption should not depend on a single briefly clear frame.
Applying it
- Estimate local density together with relative velocity, visible free space, and worst-case braking distance; degrade conservatively when a critical sensing channel weakens.
- Slow before bottlenecks, blind corners, and cross-flows. If a continuous stopping corridor is unavailable, wait outside the entrance rather than search for a gap inside.
- Validate with peak-period replay: check that every motion continuation retained a reachable stopping area and that each stop neither blocked an exit nor forced close squeezing.